This invention relates to a liquid crystal display device including a light shielding layer. The light shielding layer may be formed between picture element electrodes, or on a switching element such as a thin-film transistor. The invention also relates to a method of manufacturing liquid crystal display devices which include light shielding layers.
Published Unexamined Japanese Patent Application (PUPA) No. 62-145218 describes a display device fabricated by forming a common electrode on a first of two glass substrates, forming picture element electrodes and a thin-film transistor on the second substrate, and forming a light shield on the first glass substrate. The shade layer is designed to shade the gaps between the picture element electrodes and the area of the thin-film transistor on the second electrode. The space between the glass substrates is filled with liquid crystals materials.
Since the display device disclosed in PUPA 62-145218 has the light shielding layer formed on the glass substrate opposite the glass substrate on which the picture element electrodes and the thin-film transistors are formed, highly accurate alignment is required on assembling the two glass substrates. Further, the substrates may become misaligned when they are bonded together due to assembly conditions. In addition, light entering through the picture element electrodes may be reflected by the light shield, hitting the thin film transistors which may result in current leakage.
Published Unexamined Japanese Patent Application (PUPA) No. 62-227120 describes the formation of a light shielding layer. The light shielding layer described has a pattern corresponding to the pattern of the non-display area on a transparent substrate. The transparent substrate has a transparent electrode with a pattern corresponding to the pattern of the display area. In one embodiment, the light shielding layer is formed by screen-printing a pattern on the non-display area with a black ink comprising a thermosetting acrylic resin in which a carbon black pigment is dispersed. In a second embodiment, the light shielding layer is formed by screen-printing the shape of the pattern of non-display area with a polyimide solution in which a carbon black pigment is dispersed.
Since the light shielding layer described in PUPA 62-227120 is printed, it is difficult to accurately locate the light shield. Further, defects resulting from inaccurate printing increase as the display area decreases.
Published Unexamined Japanese Patent Application (PUPA) No. 62-253123 describes the formation of an array of electrodes on a transparent substrate wherein the electrodes consist of a transparent conducting material which is coated with an opaque layer. A light shielding layer is formed by applying a dyeable negative type photoresist evenly to the surface of the transparent substrate which includes the array of electrodes, and exposing the photoresist from the opposite side of the transparent substrate. The exposed photoresist is then developed and removed. Finally, the remaining photoresist is dyed.
Since the light shielding layer disclosed in PUPA 62-253123 is formed by the dyeing method, there are problems resulting from the dye. The dye molecules may enter into and swell the base material on dyeing, which makes the film too thick to realize the optical density required by a light shield (i.e. an O.D. greater than or equal to 2.5). Further, such light shielding layers do not resist high temperatures.
Published Unexamined Japanese Patent Application (PUPA) No. 56-107287 discloses a display device employing a thin film of amorphous silicon as a switching element which drives the liquid crystals. A metal film is used to prevent light from entering into the thin amorphous silicon film.
Since the light shielding layer disclosed in PUPA 56-107287 is formed of a metal, etching is required which may damage picture element electrodes and data wiring.